U.S. Pat. No. 6,452,381 corresponding to JP-A-H11-237256 discloses a rotation detection sensor for detecting a rotational position of a rotating body with gear teeth. This type of rotation detection sensor includes a bias magnet and two magnetic sensors. The bias magnet produces a magnetic field directed to the gear teeth of the rotating body. When the rotating body rotates, the magnetic field changes with movement between crest and root of the gear teeth. Each magnetic sensor detects the change in the magnetic field and output a sensor signal having a different phase. The rotational position of the rotating body is detected based on the sensor signals.
As described above, at least two magnetic sensors are required to detect a rotational position of a rotating body. Likewise, at least two magnetic sensors are required to detect a rotational direction of the rotating body. Therefore, when the rotation detection sensor is configured to detect both rotational position and direction of the rotating body, the rotation detection sensor needs at least four magnetic sensors. Since the number of the magnetic sensors included in the rotation detection sensor increases, the size of the rotation detection sensor increases accordingly.